1. Field of the Invention
The present invention relates to a swing-type check valve for use in pipelines. The invention, more particularly, concerns a check valve in combination with a piston/cylinder assembly for actuating the valve. The valve has particular applications in submerged pipelines where it simplifies tasks such as pigging.
2. Description of the Prior Art
The most common type of check valve is a swing check valve consisting of a hinged clapper assembly mounted inside a pipeline. The clapper assembly generally includes a clapper valve and a clapper arm which suspends the clapper valve from the valve body. When there is no flow in the pipeline, the clapper valve portion of the assembly hangs vertically suspended, in the closed position. As fluid flows through the pipeline in the desired direction, the fluid pressure swings the clapper valve partially open. When fluid tries to flow in the undesired direction, the reversed fluid pressure presses the check valve shut, thereby stopping such flow.
During normal pipeline maintenance operations, there are times when it is desirable to hold a check valve completely open. A typical time is when a pig is run through the pipeline. This operation is known as pigging. In conventional check valves, the clapper is suspended from a shaft whose ends extend out through the wall of the pipeline. The clapper can then be rotated from a fully-closed to a fully-open position by rotating the shaft. During pigging operations, a large wrench or other operator is placed on one end of the shaft and rotated until the clapper is fully opened.
In subsea pipelines, a highly trained diver must be sent down to open a check valve with the large wrench or other operator. This procedure is time consuming and involves a substantial degree of risk to the diver, particularly in a hostile ocean environment such as the North Atlantic.
Another drawback of conventional check valves is the fact that the large shaft from which the clapper is suspended penetrates the pipeline twice. This results in two pressure-boundary penetrations equal in size to the shaft cross-sectional area. In a pressurized system, it is highly desirable to minimize the number and area of such penetrations so as to not reduce the integrity of the pressurized system.